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07-02-2012, 03:54 PM
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Join Date: Mar 2005
Location: Elkhart, Indiana
Posts: 1,186
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EGTs -- How high is TOO high?
I was going to tag along on another thread, but I'm hoping that there are others out there with similar questions who might benefit from starting with a clean thread. I'll be the goat who asks the stupid question -- how high is TOO high for EGTs?
Here are the particulars: AeroSport IO-360M1 with LSE Plasma II+ on R, mag on L. Dynon EFIS & EMS. All EGT probes are mounted 3" from exhaust flanges.
My typical cruise readout at 2350rpm/22" MP at 56*F OAT show CHTs from 333* - 349* and EGTs from 1282* - 1398*, burning 8.4 gph. The CHTs have always been within about 15* of each other.
I understand that EGTs can be all over the board, depending on where the probes are mounted and other factors, but I've always kept the cruise EGT on #1 cylinder (always the hottest) at or below 1400*, except on takeoff and climbout. In fact, I have never leaned to peak.
In my old Yankee, with almost no engine instrumentation, I would pull back the mixture until the engine ran rough, then push it back in a tad and be done with it. If I did that with this plane, I'm sure that the #1 EGT would climb past 1500*.
My questions then would be:
1) If EGTs are arbitrary due to probe placement, how significant are they?
2) As long as CHTs are below 400*, is the engine OK despite high EGT readings?
3) Should I ignore my EGT readings just once and lean the engine until it stumbles, then richen it again to smooth and see just how high my #1 EGT will actually go?
4) If I do that and peak EGT is 1500 or even higher, is there anything wrong with that as long as CHTs are all good?
Obviously, all the talk about running LOP or ROP are meaningless when I can't even bring myself to lean the engine to peak because of high EGT readings. I would love to bring down my fuel flows but don't want to hurt the engine in the process.
Input is appreciated. 
__________________
Don McNamara
Peoria, AZ
Builder: RV-8 "Smokey"
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07-02-2012, 04:00 PM
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Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,271
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Don
Answers are,
Significant but not the absolute value.
No!!!!
No.
No! Don't do that either.
The answer lies in education.
I am using my iPad to type this so I will follow up later with details, but first thing to do is sign up for at least an online course from APS.
Your world will change. Better still do that and book into the live course in a few weeks.
Expect a pm too,
Regards
David
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07-02-2012, 04:52 PM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Don,
No such thing as "too high". Per Lycoming you can set max EGT at cruise power, thus any EGT less than peak is obviously fine, ROP or LOP, depending on your desire for power or economy.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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07-02-2012, 07:37 PM
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Join Date: Jan 2005
Location: Arkansas
Posts: 571
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Follow up question for Dan
Dan, following on the discussion and this may be a dumb question but if CHTs never exceed limits is it possible to burn a valve ? Reason I am asking is that I was wondering if you had a carbed engine but were trying to run LOP and the CHTs were 50 to 100 degrees apart but not exceeding 400 or so,..... is there any chance of doing damage. Maybe one cyl on the lean side and one on the peak but CHTs still good. No problem watching that with the engine monitor.
In short, if you never exceed CHT limits on any cyl, can you damage the engine ?
Hope you can make Petit Jean!
Thanks Bill
7a with a new suit :-)
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07-02-2012, 09:45 PM
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Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,271
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The answer is you can do damage at below 400F, however most damage is caused by poor valve / seat fit. Other than that if you ran high power settings and only a bit LOP, I doubt you could create problems.
There is a good reason to have all cylinder monitors and a good knowledge to understand what it is telling you.
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07-03-2012, 05:05 AM
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Join Date: May 2005
Location: Florida
Posts: 774
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I have always run our planes at LOP by leaning at altitude until engine stumble and then turning mixture in 1 full turn. This GENERALLY produces a temp of about 1450 on the hottest EGT. I run 2350 to 2420 RPM's and have had no problems. All three of my RV's have been run the same way and the engines have gone beyond TBO with no problem. Lycomings like to be pushed a bit.
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07-03-2012, 05:21 AM
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Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,271
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Woodie
That probably works just fine.
Even though you may not know why, you have been fine, even if for the wrong reasons.
On most IO320 or 360, and for that matter O-320/360 and with a fixed pitch prop, if you are at altitude, and say 2450-2500 and lean until the RPM drops, you are probably at peak on the richest and the rest LOP, so that works fine.
If at altitude, say 5500+ and you can get to your 65% rating by fuel flow. You Are FINE
HP x 0.65 = 65% power
Then divide that HP by 14.9 = GPH
If you can get to this number..... you are fine!
But I must say.....there is more to engine management than just setting a fuel flow.
You really need to invest in your education. 
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07-03-2012, 07:07 AM
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Join Date: Jun 2008
Location: Hilton, South Africa
Posts: 25
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Can EGT's ever be too high?
My understanding of EGT is this. The temp of combustion in your engine is based on the ratio of fuel/air upon ignition. The more you lean from rich the less fuel you mix with the same air volume. At the point where this ratio is at its optimum, best power is produced, as well as the combustion temp being the hottest. Thereafter as you lean more the combustion temp declines as the mixture becomes too lean, as well as power output reducing.
The engine starts to run rough when the volume of fuel to air becomes leaned to the point that the combustion becomes marginal and lacking in intensity. An associated lowering of combustion temperature occurs in this, the LOP environment.
The reason why these values are different in our engines is because the measuring system (probes, their relative position in the exhaust header and the differing performance of the probe itself) and the relative differences in fuel quantity each cylinder is receiving, are very rarely the same.
Please give me some guidance if this is a wrong viewpoint, or too simple in its content
__________________
Gary Keyser
RV-7 Sold
RV-9A QB Finishing
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07-03-2012, 07:09 AM
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Join Date: Mar 2005
Location: Elkhart, Indiana
Posts: 1,186
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Arrrrgggh!
Quote:
Originally Posted by RV10inOz
...Even though you may not know why, you have been fine, even if for the wrong reasons ....
...But I must say.....there is more to engine management than just setting a fuel flow.
You really need to invest in your education. 
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After reviewing some more threads on the subject, David, I see that there are some rather strong opinions on the matter.
What is your relationship with APS? Are you a lecturer, consultant, owner, investor or simply a fan? I ask because anytime I see a financial commitment in a recommendation I like to make sure I know if the recommendation is based on any financial considerations.
And, pertaining to my original questions, perhaps I should refine or amend them. As ignorant as this will sound, one of my frustrations with previous threads on LOP operation has been with the depth of the discussions by engineering types. I really have little interest in obtaining a graduate degree in engine technology. Yes, a basic understanding of HOW and WHY things work is important, but correctly operating a 4-cylinder, horizontally-opposed, air-cooled, reciprocating engine really can't be that difficult, can it?
My questions boil down to EGT readings. My #1 EGT is hotter than the others by 100-200 degrees, which is apparently not that unusual. And, given the variability of installations, the readings are somewhat arbitrary compared with CHTs.
*sigh* The more I think through the issue, the more frustrated I am becoming. I don't even know how to accurately phrase the question without starting some kind of war between the LOP and the ROP adherents.
IF I decide to experiment with LOP or ROP operations, at what EGT reading of my hottest cylinder (#1) should I be concerned? When I was breaking in the engine (which is apparently another argumentative issue), I relied on my Dynon EMS %power readout to keep things at 75% or above, and wasn't concerned about EGTs.
However, now that the engine has over 200 hours on it, I thought that I should learn to properly lean the engine and run it more efficiently -- but that #1 EGT worries me when it climbs above 1400*.
Perhaps I should unplug the EMS and just fly the stupid plane ... sometimes too much information is ... well, too much. 
__________________
Don McNamara
Peoria, AZ
Builder: RV-8 "Smokey"
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07-03-2012, 07:22 AM
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Join Date: Sep 2006
Location: Townsend, Montana
Posts: 3,179
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Quote:
Originally Posted by N8RV
Perhaps I should unplug the EMS and just fly the stupid plane ... sometimes too much information is ... well, too much. 
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When I was first breaking in my engine and getting it dialed in, A very sharp A&P told me.
"well it seems the only problems I can find with your engine operation is You" "quit looking at all that info" "get up to cruise, set your prop, pull the mixture until rough and nudge it back in"
I started doing just that then I started looking at the info again...guess what I running 60-70%power. Usually running right near Peak, but it isn't a problem at that power level.
__________________
Retired Dam guy. Life is good.
Brian, N155BKsold but bought back.
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